field evaluation of air-blocking shelf for dust control on ... surface mine dust... · silica dust...
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OMSHR Office of Mine Safety and Health Research
Silica dust controls for surface mines
Randy Reed
Dust, Ventilation, and Toxic Substances Branch
Best Practices for Controlling Respirable Dust in Coal Mines October 28, 2014
Office of Mine Safety and Health Research
Outline
Drilling
Cabs
Hauling
Crusher dump point
EVADE/HelmetCAM
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Dust Emissions From
Blasthole Drills
• 52% - Drill deck
– 28% shroud
– 24% table bushing
• 38% - Collector dumping
• 10% - Other mining equipment sources
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Typical Dust Concentrations
Encountered • Drill Deck (Shroud &
Table Bushing)
– Peak conc. can reach
98 mg/m3
• Dust Collector
– Peak conc. can reach
68 mg/m3
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Drilling Dust Control
• Wet Drilling
– Use of water combined with
air to flush drill cuttings
– Prevents dust generation
during drilling
• Dry Drilling
– No water used in bailing air
– Use of a dust collector to
prevent dust generation
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Wet Drilling
• Best Drilling Dust Control
• Does not require large amounts of water
• Wet drilling eliminates up to 97% respirable dust
• Rotary bit degradation
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Wet Drilling
Potential problems:
– Bit Degradation (hydrogen embrittlement)
– Cold climates (water freezing)
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Water Separator Sub Increases Roller
Bit Life
Bit life increased 4.5 times
with use of separator sub
9000 ft with sub
2000 ft without sub
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Small Diameter Water Separator Sub Study
Wet vs Dry Drilling
0.0
100.0
200.0
300.0
400.0
500.0
600.0
dry wet
Co
ncen
tra
tio
n, m
g/m
3
Wet
Dry
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Dry Drilling
• Use of dust collector
• Can be up to 99% efficient
– Properly maintained
– Operated correctly
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Dry Drilling Dust Control Solutions
• Proper maintenance of dust collector system
• Maintain high collector airflow to bailing airflow ratios
– 3:1 or more; collector airflow 3 x bailing airflow
• Prevent/reduce drill deck shroud leakage
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Drill Shroud Leakage
Maintain tight shroud enclosure with the ground
(unlike this example)
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Airflow Patterns Underneath Drill
Shroud
Normal airflow patterns Airflow patterns w/ shelf
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Horizontal Shelf
• Mine A – 69-70% reductions area
surrounding drill • Variation dependent upon wind
direction
– 66% reduction at shroud location
• Mine B – Low dust concentrations
surrounding drill • For both shelf-off/shelf-on
– 81% reduction at shroud location
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Adjustable Height Shroud
Dust emissions below 0.5 mg/m3
Angle Drill Shroud
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Collector Exhaust Port Dust Control
• Replace dust collector filters
• Stand away from drill
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Dust Collector Dump Shroud
63 – 88% reduction
0.53 – 1.34 mg/m3 0.16 – 0.24 mg/m3
Easy installation, Little maintenance
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Enclosed Cab Filtration Systems
• Integrated into HVAC
Systems
• Protection Factors Vary
(PF= Coutside /Cinside)
– Drills 2.5 to 84
– Bulldozers 0 to 45
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Protection Factor, Efficiency, &
Penetration • Protection Factor (PF) = Coutside /Cinside
– C = dust concentration (mg/m3)
– The bigger the number the better
• Efficiency (η) = (Coutside-Cinside)/Coutside
– Range 0 – 1
– 0 = bad, 1 = good
• Penetration (Pen) = 1-η
– Range 0 – 1
– 1 = bad, 0 = good
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Refurbish Cabs
• Ceiling mount heating and AC units
• External filter and fan units
• Improve cab enclosure seals
• Ensure good cab integrity
• Positive pressurization
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Utilize High Efficiency Respirable Dust
Filters
• Intake filter >
95% on
respirable-sized
dusts
• Use an efficient
recirculation filter • Improves cab
protection factor
• Reduces stability
time
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Minimize Dust Sources in Cab
• Use good housekeeping
practices
• Remove floor heaters
– Floor heater use increased dust
levels from 0.03 to 0.26 mg/m3
• Rubber mats better than
carpeting
• Gritless sweeping compounds
*non-petroleum based*
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Keep Doors Closed During Equipment
Operation
• 0.81 mg/m3 when briefly opened to add
drill steels
• 0.09 mg/m3 with
door closed
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Controlling Haul Road Dust
• ≈15% of
airborne dust
< 10 µm
• ≈4% of
airborne dust
< 3.5 µm
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Dust Dissipation Effect
Increase distance between vehicles
0.0
1.0
2.0
3.0
4.0
5.0
-15 0 15 30 45 60 75Time Period Around Truck Passage, sec.
Respirable
Dust
Concentr
ation,
mg/m
3
Road Berm 50 ft 100 ft
Time Truck Exited Sampling Grid
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Treatment of Unpaved Road Surface
• Water effective with reapplications
• Alternative road treatments – Salts, surfactants, soil cements, bitumens, films (polymers) may extend time of
effectiveness
– Application requirements
– Selection of treatment site specific
0
2
4
6
8
10
12
10:00:01 11:00:01 12:00:01 13:00:01 14:00:01 15:00:01 16:00:01
Time, hr:min:sec
Re
sp
ira
ble
Du
st
Le
ve
l, m
g/m
3
Road Drying Out
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Crusher Hopper Dump Points
• Enclose dump point
• Water sprays
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Enclose Hopper Dump Point
• Staging curtains
reduce dust
escape
• Exhaust
ventilation
systems may be
used, but must be
properly designed
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Water Spray Use
• Amount of water to use
– Initially, apply water to obtain 1% moisture content
• Use automated spray system
– Conserve water use
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Prevent Dust Rollback Underneath
Vehicle
• Tire stop
reduces dust
rollback
• Water sprays
redirect dust
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EVADE/HelmetCAM
• Dust source identification
– HelmetCAM field survey
• Coal miners
• Metal/nonmetal miners
– EVADE software for analysis
• NIOSH developed
• Develop control strategies
– Target dust sources to reduce
over-exposures of miners
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EVADE/HelmetCAM • Video Cameras
– Attach to hardhat
– Video length limited to battery life
– File types AVI, WMV, or MP4
V.I.O. $300 - $400
Contour Approximately $200
Go Pro $200 - $400
Mention of any company or product does not constitute endorsement by the
National Institute for Occupational Safety and Health (NIOSH)
Office of Mine Safety and Health Research
EVADE/HelmetCAM
• Dust monitors
– Worn on belt
– Provide
instantaneous dust
concentrations
– Any device where
data can be stored
as Excel CSV file Thermo pDR-1000 Thermo pDR-1500
TSI AM-510
Mention of any company or product does not constitute endorsement by the
National Institute for Occupational Safety and Health (NIOSH)
Office of Mine Safety and Health Research
Three Options to House Helmet-CAM
Backpack/Miner’s Safety Belts/Safety Vest
EVADE/HelmetCAM
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EVADE software/HelmetCAM
Methodology http://www.cdc.gov/niosh/mining/Works/coversheet1867.html
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Summary • Wet Drilling
– Dust control efficiency 97% • Little water required
• Water separator sub
• Dry Drilling
– Dust control efficiency 99% • Properly maintained
• Operated correctly – Minimize leakage
– 3:1 collector to bailing airflow ratio or greater
– Horizontal shelf, angle drill shroud, dust collector dump shroud, etc.
• Operator Cabs
– Properly maintained • Maintain seals, filters, etc.
• Ceiling mount HVAC systems
– Operate correctly • Positive pressure
• Housekeeping
• Recirculation filter
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Summary
• Hauling – Water effectively controls
road dust
– Surfactants may be effective
• Crusher dump point – Enclose dump point
– Use water sprays
• EVADE/HelmetCAM – Identify dust sources
– Target dust control development
Office of Mine Safety and Health Research
Dust Control Handbook for Industrial Minerals
Mining and Mineral Processing
http://www.cdc.gov/niosh/mining/works/coversheet1765.html
www.cdc.gov/niosh/mining
Office of Mine Safety and Health Research
Disclaimer: The findings and conclusions in this presentation have not been formally disseminated by the National Institute for Occupational Safety and
Health and should not be construed to represent any agency determination or policy. Mention of any commercial product does not imply endorsement.
Questions???
Randy Reed
412-386-5205